CN109038515A - A kind of Hybrid HVDC route traveling-wave protection method and system based on Dual Tree Complex Wavelet variation - Google Patents

Abstract

The invention discloses a hybrid direct current transmission line traveling wave protection method and system based on dual tree complex wavelet changes, including: calculating the voltage difference modulus and voltage common modulus according to the collected positive and negative DC voltages; The wavelet transform calculates the dual tree complex wavelet transform of the voltage difference modulus, and judges whether the protection is started according to the high-sensitivity start judgment basis; when the protection is determined to start, according to the dual tree complex wavelet transform and the corresponding The fault extreme value of the hybrid DC transmission line is used to judge the fault type and carry out corresponding protection actions. The invention can quickly distinguish the faults of the hybrid direct current transmission line, and can reliably select fault poles, greatly reduces the translation sensitivity in the usual real wavelet transform, and can significantly improve the accuracy of fault analysis in long-distance transmission lines , to realize the rapid identification of hybrid DC transmission line faults.

Description

A Traveling Wave Protection Method for Hybrid HVDC Transmission Lines Based on Dual Tree Complex Wavelet Variation law and system

technical field

The present invention relates to the technical field of relay protection of electrical technology, and more specifically, relates to a hybrid direct current transmission line traveling wave protection method and system based on dual tree complex wavelet variation.

Background technique

The line commutated converter type HVDC transmission system (Line Commutated Converter, LCC-HVDC) based on thyristor technology has been widely used in long-distance large-capacity power transmission, asynchronous networking and other occasions, but it has the problem of commutation failure on the inverter side . The high-voltage DC transmission system (Voltage Source Converter, VSC-HVDC) based on the voltage source converter has been rapidly developed due to its independent control of active power and reactive power, the ability to work in passive systems, and not being affected by commutation failures. Development, but it has the disadvantages of high cost and large operation loss. Hybrid DC transmission system (LCC-VSC) is a new type of DC transmission topology, which combines the advantages of both LCC and VSC. When VSC is used at the receiving end, it can improve the operating characteristics of the AC system at the receiving end, so it is suitable for receiving The construction of the UHV DC project of the multi-infeed DC grid and the transformation of the LCC-HVDC receiving end converter station have good engineering application prospects.

Hybrid DC line protection is a key issue in the development of hybrid DC, and its main technical difficulty lies in identifying faulty sections quickly and reliably. Because the fault transient characteristics of hybrid HVDC transmission lines and the inherent composition of primary equipment are different from those of single conventional HVDC transmission and flexible HVDC transmission, the traditional AC system protection, conventional HVDC system protection and flexible HVDC system protection cannot be directly applied to Hybrid DC transmission system. In terms of algorithms, the traditional discrete wavelet transform first decomposes the input signal into high-frequency and low-frequency components, and then obtains the wavelet decomposition coefficients through double decimation, but the double decimation process of discrete wavelet transform will cause large aliasing and distortion. Seriously affect the ability of wavelet coefficients to represent the original signal features.

Contents of the invention

The invention proposes a hybrid direct current transmission line traveling wave protection method and system based on dual tree complex wavelet changes to solve the problem of how to quickly determine the fault of the hybrid direct current transmission line.

In order to solve the above problems, according to one aspect of the present invention, a hybrid DC transmission line traveling wave protection method based on dual tree complex wavelet variation is provided, characterized in that the method includes:

Calculate the voltage differential modulus and voltage common modulus according to the collected positive and negative DC voltages;

Use the dual tree complex wavelet transform to calculate the voltage difference modulus, and judge whether the protection is started according to the high sensitivity start judgment basis;

When it is determined that the protection starts, according to the dual tree complex wavelet transform of the voltage common modulus and the voltage difference modulus and the corresponding fault extreme value, the fault judgment basis of the hybrid DC transmission line is used to judge the fault type and carry out the corresponding protection action. The fault judgment basis of the hybrid DC transmission line includes: bipolar fault protection judgment basis, unipolar metallic fault protection judgment basis, unipolar transition resistance fault protection judgment basis and fault pole selection judgment basis.

Preferably, wherein the differential voltage modulus and the voltage common modulus are calculated using the following formula:

f(x)=0.5x(U ₁ −U ₂ ),

f ₁ (x)=0.5x(U ₁ +U ₂ ),

Among them, f(x) is the differential modulus of voltage; f ₁ (x) is the common modulus of voltage; U ₁ and U ₂ are the collected positive and negative DC voltages respectively.

Preferably, wherein said dual tree complex wavelet transform is used to calculate the voltage difference modulus, and judging whether the protection is started according to the high-sensitivity start judgment basis includes:

The dual tree complex wavelet transform W _S f(x) of the differential modulus is calculated by using the even number complex wavelet transform, and the high sensitivity start judgment basis is used to judge whether W _S f(x)>Δ3 is satisfied, if W _S f(x)> Δ3, it is determined that the protection is activated, and the integral value ∫U _com ³ of the third power of the voltage common mode is calculated; otherwise, it is determined that the protection is not activated; wherein, S is a scaling function; Δ3 is the third preset threshold, which is a positive value.

Preferably, where

The basis for judging the bipolar fault protection is:

If W _S f(x)>k ₁ W _S f(x ₀₁ ) holds true, it is judged as a bipolar fault of the hybrid DC transmission line;

The basis for judging the unipolar metallic fault protection is:

If k ₂ W _S f(x ₀₂ )＜W _S f(x)＜k ₁ W _S f(x ₀₁ ) holds true, it is judged as a unipolar metallic fault;

The basis for judging the unipolar transition resistance fault protection is as follows:

If k ₃ W _S f(x ₀₃ )＜W _S f(x)＜k ₂ W _S f(x ₀₂ ) holds true, then it is judged as unipolar transition resistance fault;

The fault pole selection judgment basis is as follows:

If ∫f ₁ ³ (x)＞Δ1 holds true, it is judged as a negative pole fault;

If ∫f ₁ ³ (x)<Δ2 is established, it is judged as a positive fault;

Among them, f(x) is the voltage difference modulus; W _S f(x) is the dual tree complex wavelet transform of f(x); S is the scaling function, and x ₀₁ is the dual tree complex wavelet transform of the line end bipolar fault Modulus maximum point; W _S f(x ₀₁ ) is the modulus maximum value of the dual tree complex wavelet transform at the line end bipolar fault, k ₁ is the ratio coefficient; x ₀₂ is the dual Modulus maximum point of tree complex wavelet transform; W _S f(x ₀₂ ) is the modulus maximum value of dual tree complex wavelet transform when unipolar fault occurs at the line end; k ₂ is the ratio coefficient; x ₀₃ is the single pole passing through the line end W _S f (x ₀₃ ) is the modulus maximum point of the dual tree complex wavelet transform when the single pole at the end of the line passes through the transition resistance fault; k ₃ is the ratio coefficient; f ₁ (x) is a voltage common mode value, Δ1 is a first preset threshold, which is a positive value; Δ2 is a second preset threshold, which is a negative value.

Preferably, when it is determined that the protection starts, according to the dual tree complex wavelet transform of the voltage common mode and voltage difference modulus and the corresponding fault extreme value, the fault type is judged by using the fault judgment basis of the hybrid direct current transmission line and the corresponding Protective actions, including:

If W _S f(x)>k ₁ W _S f(x ₀₁ ) holds true, it is judged as a bipolar fault of the hybrid DC transmission line, and the traveling wave protection of the positive and negative poles operates quickly;

If k ₂ W _S f(x ₀₂ )＜W _S f(x)＜k ₁ W _S f(x ₀₁ ) holds true, then it is judged as a unipolar metallic fault, and the polarity of the fault is judged by using the fault pole selection judgment basis , if ∫f ₁ ³ (x)＞Δ1 holds true, it is judged as a negative pole fault, and the negative pole traveling wave protection operates quickly; if ∫f ₁ ³ (x)<Δ2 holds true, it is judged as a positive pole fault, and the positive pole traveling wave protection operates quickly ;

If k ₃ W _S f(x ₀₃ )＜W _S f(x)＜k ₂ W _S f(x ₀₂ ) holds true, it is judged as a unipolar transition resistance fault, and the fault is judged based on the fault pole selection judgment basis polarity, if ∫f ₁ ³ (x)>Δ1 is established, it is judged as a negative pole fault, and the negative pole traveling wave protection acts quickly; if ∫f ₁ ³ (x)<Δ2 is established, it is judged as a positive pole fault, and the positive pole traveling wave Protection for quick action.

According to another aspect of the present invention, a hybrid DC transmission line traveling wave protection system based on dual tree complex wavelet variation is provided, wherein the system includes:

A calculation unit, used to calculate the voltage differential modulus and the voltage common modulus according to the collected positive and negative DC voltages;

The judging unit is used to calculate the dual tree complex wavelet transform of the voltage difference modulus by using the dual tree complex wavelet transform, and judge whether the protection is started according to the high-sensitivity start judgment basis;

The protection unit is used for judging the fault type according to the dual tree complex wavelet transform of the voltage common modulus and the voltage differential modulus and the corresponding fault extreme value using the fault judgment basis of the hybrid direct current transmission line when the protection is started and performing corresponding protection Action, wherein the fault judgment basis of the hybrid DC transmission line includes: bipolar fault protection judgment basis, unipolar metallic fault protection judgment basis, unipolar transition resistance fault protection judgment basis and fault pole selection judgment basis.

Preferably, in the calculation unit, the voltage differential modulus and the voltage common modulus are calculated using the following formula:

f(x)=0.5x(U ₁ −U ₂ ),

f ₁ (x)=0.5x(U ₁ +U ₂ ),

Among them, f(x) is the differential modulus of voltage; f ₁ (x) is the common modulus of voltage; U ₁ and U ₂ are the collected positive and negative DC voltages respectively.

Preferably, in the judging unit, the dual tree complex wavelet transform is used to calculate the voltage differential modulus, and the judgment whether the protection is started is judged according to the high-sensitivity start judgment basis, including:

The dual tree complex wavelet transform W _S f(x) of the differential modulus is calculated by using the even number complex wavelet transform, and the high sensitivity start judgment basis is used to judge whether W _S f(x)>Δ3 is satisfied, if W _S f(x)> Δ3, it is determined that the protection is activated, and the integral value ∫U _com ³ of the third power of the voltage common mode is calculated; otherwise, it is determined that the protection is not activated; wherein, S is a scaling function; Δ3 is the third preset threshold, which is a positive value.

Preferably, where

The basis for judging the bipolar fault protection is:

If W _S f(x)>k ₁ W _S f(x ₀₁ ) holds true, it is judged as a bipolar fault of the hybrid DC transmission line;

The basis for judging the unipolar metallic fault protection is:

If k ₂ W _S f(x ₀₂ )＜W _S f(x)＜k ₁ W _S f(x ₀₁ ) holds true, it is judged as a unipolar metallic fault;

The basis for judging the unipolar transition resistance fault protection is as follows:

If k ₃ W _S f(x ₀₃ )＜W _S f(x)＜k ₂ W _S f(x ₀₂ ) holds true, then it is judged as unipolar transition resistance fault;

The fault pole selection judgment basis is as follows:

If ∫f ₁ ³ (x)＞Δ1 holds true, it is judged as a negative pole fault;

If ∫f ₁ ³ (x)<Δ2 is established, it is judged as a positive fault;

Among them, f(x) is the voltage difference modulus; W _S f(x) is the dual tree complex wavelet transform of f(x); S is the scaling function, and x ₀₁ is the dual tree complex wavelet transform of the line end bipolar fault Modulus maximum point; W _S f(x ₀₁ ) is the modulus maximum value of the dual tree complex wavelet transform at the line end bipolar fault, k ₁ is the ratio coefficient; x ₀₂ is the dual Modulus maximum point of tree complex wavelet transform; W _S f(x ₀₂ ) is the modulus maximum value of dual tree complex wavelet transform when unipolar fault occurs at the line end; k ₂ is the ratio coefficient; x ₀₃ is the single pole passing through the line end W _S f (x ₀₃ ) is the modulus maximum point of the dual tree complex wavelet transform when the single pole at the end of the line passes through the transition resistance fault; k ₃ is the ratio coefficient; f ₁ (x) is a voltage common mode value, Δ1 is a first preset threshold, which is a positive value; Δ2 is a second preset threshold, which is a negative value.

Preferably, in the protection unit, when it is determined that the protection is started, according to the dual tree complex wavelet transform of the voltage common modulus and the voltage differential modulus and the corresponding fault extreme value, the fault judgment basis of the hybrid direct current transmission line is used to judge the fault type And carry out corresponding protective actions, including:

If W _S f(x)>k ₁ W _S f(x ₀₁ ) holds true, it is judged as a bipolar fault of the hybrid DC transmission line, and the traveling wave protection of the positive and negative poles operates quickly;

If k ₂ W _S f(x ₀₂ )＜W _S f(x)＜k ₁ W _S f(x ₀₁ ) holds true, then it is judged as a unipolar metallic fault, and the polarity of the fault is judged by using the fault pole selection judgment basis , if ∫f ₁ ³ (x)＞Δ1 holds true, it is judged as a negative pole fault, and the negative pole traveling wave protection operates quickly; if ∫f ₁ ³ (x)<Δ2 holds true, it is judged as a positive pole fault, and the positive pole traveling wave protection operates quickly ;

If k ₃ W _S f(x ₀₃ )＜W _S f(x)＜k ₂ W _S f(x ₀₂ ) holds true, it is judged as a unipolar transition resistance fault, and the fault is judged based on the fault pole selection judgment basis polarity, if ∫f ₁ ³ (x)>Δ1 is established, it is judged as a negative pole fault, and the negative pole traveling wave protection acts quickly; if ∫f ₁ ³ (x)<Δ2 is established, it is judged as a positive pole fault, and the positive pole traveling wave Protection for quick action.

The present invention provides a hybrid direct current transmission line traveling wave protection method and system based on dual tree complex wavelet transformation. The dual tree complex wavelet transform is used to extract the middle and high frequency transient components of the decoupled voltage differential modulus for traveling wave protection. Compared with the traveling wave protection currently applied to conventional DC transmission and flexible DC transmission lines, it can quickly distinguish the faults of hybrid DC transmission lines, and can reliably select fault poles, greatly reducing the usual real wavelet transform. Translate sensitivity, realize accurate extraction of high-frequency components of sampling data within a short data window, solve the problem of insufficient long-distance sensitivity of existing protection, and can significantly improve the accuracy of fault analysis in long-distance transmission lines, and realize hybrid DC transmission line faults rapid identification.

Description of drawings

A more complete understanding of the exemplary embodiments of the present invention can be had by referring to the following drawings:

1 is a flow chart of a hybrid DC transmission line traveling wave protection method 100 based on dual tree complex wavelet changes according to an embodiment of the present invention;

Fig. 2 is a schematic structural diagram of a hybrid direct current transmission line traveling wave protection system 200 based on dual tree complex wavelet variation according to an embodiment of the present invention.

Detailed ways

Exemplary embodiments of the present invention will now be described with reference to the drawings; however, the present invention may be embodied in many different forms and are not limited to the embodiments described herein, which are provided for the purpose of exhaustively and completely disclosing the present invention. invention and fully convey the scope of the invention to those skilled in the art. The terms used in the exemplary embodiments shown in the drawings do not limit the present invention. In the figures, the same units/elements are given the same reference numerals.

Unless otherwise specified, the terms (including scientific and technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it can be understood that terms defined by commonly used dictionaries should be understood to have consistent meanings in the context of their related fields, and should not be understood as idealized or overly formal meanings.

Fig. 1 is a flow chart of a method 100 for traveling wave protection of a hybrid direct current transmission line based on dual tree complex wavelet variation according to an embodiment of the present invention. As shown in Figure 1, the hybrid DC transmission line traveling wave protection method based on the dual tree complex wavelet transformation according to the embodiment of the present invention uses the dual tree complex wavelet transform to extract the high-frequency transient components of the decoupled voltage differential modulus for traveling wave protection , compared with the current traveling wave protection applied to conventional HVDC and flexible HVDC transmission lines, this method can quickly distinguish the faults of hybrid HVDC transmission lines, and can reliably select fault poles, greatly reducing the usual real wavelet The translational sensitivity in the transformation realizes the accurate extraction of the high-frequency components of the sampling data in the short data window, solves the problem of insufficient long-distance sensitivity of existing protection, can significantly improve the accuracy of fault analysis in long-distance transmission lines, and realizes hybrid DC Rapid identification of transmission line faults. The hybrid DC transmission line traveling wave protection method 100 based on dual tree complex wavelet changes provided by the embodiment of the present invention starts from step 101, and calculates the voltage differential modulus and voltage common mode according to the collected positive and negative DC voltages in step 101 quantity.

Preferably, wherein the differential voltage modulus and the voltage common modulus are calculated using the following formula:

f(x)=0.5x(U ₁ −U ₂ ),

f ₁ (x)=0.5x(U ₁ +U ₂ ),

Among them, f(x) is the differential modulus of voltage; f ₁ (x) is the common modulus of voltage; U ₁ and U ₂ are the collected positive and negative DC voltages respectively.

Preferably, in step 102, the dual tree complex wavelet transform is used to calculate the voltage difference modulus by using the dual tree complex wavelet transform, and whether the protection is activated is judged according to the high-sensitivity start judgment basis.

Preferably, wherein said dual tree complex wavelet transform is used to calculate the voltage difference modulus, and judging whether the protection is started according to the high-sensitivity start judgment basis includes:

The dual tree complex wavelet transform W _S f(x) of the differential modulus is calculated by using the even number complex wavelet transform, and the high sensitivity start judgment basis is used to judge whether W _S f(x)>Δ3 is satisfied, if W _S f(x)> Δ3, it is determined that the protection is activated, and the integral value ∫U _com ³ of the third power of the voltage common mode is calculated; otherwise, it is determined that the protection is not activated; wherein, S is a scaling function; Δ3 is the third preset threshold, which is a positive value.

Preferably, in step 103, when it is determined that the protection is activated, according to the dual tree complex wavelet transform of the voltage common modulus and the voltage differential modulus and the corresponding fault extreme values, the fault type is judged by using the fault judgment basis of the hybrid direct current transmission line and corresponding Protection action, wherein the fault judgment basis of the hybrid direct current transmission line includes: bipolar fault protection judgment basis, unipolar metallic fault protection judgment basis, unipolar transition resistance fault protection judgment basis and fault pole selection judgment basis.

Preferably, where

The basis for judging the bipolar fault protection is:

If W _S f(x)>k ₁ W _S f(x ₀₁ ) holds true, it is judged as a bipolar fault of the hybrid DC transmission line;

The basis for judging the unipolar metallic fault protection is:

If k ₂ W _S f(x ₀₂ )＜W _S f(x)＜k ₁ W _S f(x ₀₁ ) holds true, it is judged as a unipolar metallic fault;

The basis for judging the unipolar transition resistance fault protection is as follows:

If k ₃ W _S f(x ₀₃ )＜W _S f(x)＜k ₂ W _S f(x ₀₂ ) holds true, then it is judged as unipolar transition resistance fault;

The fault pole selection judgment basis is as follows:

If ∫f ₁ ³ (x)＞Δ1 holds true, it is judged as a negative pole fault;

If ∫f ₁ ³ (x)<Δ2 is established, it is judged as a positive fault;

Among them, f(x) is the voltage difference modulus; W _S f(x) is the dual tree complex wavelet transform of f(x); S is the scaling function, and x ₀₁ is the dual tree complex wavelet transform of the line end bipolar fault Modulus maximum point; W _S f(x ₀₁ ) is the modulus maximum value of the dual tree complex wavelet transform at the line end bipolar fault, k ₁ is the ratio coefficient; x ₀₂ is the dual Modulus maximum point of tree complex wavelet transform; W _S f(x ₀₂ ) is the modulus maximum value of dual tree complex wavelet transform when unipolar fault occurs at the line end; k ₂ is the ratio coefficient; x ₀₃ is the single pole passing through the line end W _S f (x ₀₃ ) is the modulus maximum point of the dual tree complex wavelet transform when the single pole at the end of the line passes through the transition resistance fault; k ₃ is the ratio coefficient; f ₁ (x) is a voltage common mode value, Δ1 is a first preset threshold, which is a positive value; Δ2 is a second preset threshold, which is a negative value.

Preferably, when it is determined that the protection starts, according to the dual tree complex wavelet transform of the voltage common mode and voltage difference modulus and the corresponding fault extreme value, the fault type is judged by using the fault judgment basis of the hybrid direct current transmission line and the corresponding Protective actions, including:

If W _S f(x)>k ₁ W _S f(x ₀₁ ) holds true, it is judged as a bipolar fault of the hybrid DC transmission line, and the traveling wave protection of the positive and negative poles operates quickly;

If k ₂ W _S f(x ₀₂ )＜W _S f(x)＜k ₁ W _S f(x ₀₁ ) holds true, then it is judged as a unipolar metallic fault, and the polarity of the fault is judged by using the fault pole selection judgment basis , if ∫f ₁ ³ (x)＞Δ1 holds true, it is judged as a negative pole fault, and the negative pole traveling wave protection operates quickly; if ∫f ₁ ³ (x)<Δ2 holds true, it is judged as a positive pole fault, and the positive pole traveling wave protection operates quickly ;

If k ₃ W _S f(x ₀₃ )＜W _S f(x)＜k ₂ W _S f(x ₀₂ ) holds true, it is judged as a unipolar transition resistance fault, and the fault is judged based on the fault pole selection judgment basis polarity, if ∫f ₁ ³ (x)>Δ1 is established, it is judged as a negative pole fault, and the negative pole traveling wave protection acts quickly; if ∫f ₁ ³ (x)<Δ2 is established, it is judged as a positive pole fault, and the positive pole traveling wave Protection for quick action.

Under normal circumstances, W _S f(x)<Δ3, the high-sensitivity starting judgment basis does not start, and the traveling wave protection of the hybrid DC transmission line is reliable and does not operate.

When the fault occurs in the bipolar zone of the hybrid HVDC transmission line, W _S f(x)>k ₁ W _S f(x ₀₁ ), the traveling wave protection of the hybrid HVDC transmission line operates quickly.

When the metallic fault occurs in the unipolar region of the hybrid DC transmission line, k ₂ W _S f(x ₀₂ )<W _S f(x)<k ₁ W _S f(x ₀₁ ), after the judgment basis of fault pole selection, the hybrid DC Traveling wave protection of transmission lines operates quickly.

When there is a transition resistance fault in the unipolar area of the hybrid DC transmission line, k ₃ W _S f(x ₀₃ )<W _S f(x)<k ₂ W _S f(x ₀₂ ), after the fault pole selection judgment basis, the hybrid DC Traveling wave protection of transmission lines operates quickly.

When W _S f(x)<k ₃ W _S f(x ₀₃ ) is faulted outside the hybrid DC transmission line, the traveling wave protection of the hybrid DC transmission line is reliable and does not operate.

In an embodiment of the present invention, the hybrid DC transmission line traveling wave protection method based on dual tree complex wavelet transform, the specific steps are as follows:

Step1, collect positive and negative DC voltages U ₁ and U ₂ .

Step 2, calculate voltage differential modulus U _dif =0.5×(U ₁ −U ₂ ) and U _com =0.5×(U ₁ +U ₂ ).

Ste3, use the even complex wavelet transform to calculate the differential modulus W _S U _dif , compare the size of W _S U _dif with Δ3, if W _S f(x) > Δ3, then the protection starts, and at the same time start to calculate ∫U _com ³

Step4, compare W _S U _dif with k ₁ W _S f(x ₀₁ ), if W _S U _dif >k ₁ W _S f(x ₀₁ ), it is judged that the hybrid DC transmission bipolar line is faulty, and the positive and negative lines Traveling wave protection is fast acting.

If k ₂ W _S f(x ₀₂ )<W _S U _dif <k ₁ W _S f(x ₀₁ ) satisfies ∫U _com ³ >Δ1 at the same time, it is judged to be a metallic fault of the negative pole of the hybrid HVDC transmission line, and the traveling wave of the negative pole line The protection acts quickly; if k ₂ W _S f(x ₀₂ )<W _S U _dif <k ₁ W _S f(x ₀₁ ) meets ∫U _com ³ <Δ2 at the same time, it is judged as a metallic fault of the positive pole line of the hybrid DC transmission, Fast acting positive line traveling wave protection.

If k ₃ W _S f(x ₀₃ )<W _S U _dif <k ₂ W _S f(x ₀₂ ) satisfies ∫U _com ³ >Δ1 at the same time, it is judged that the hybrid HVDC negative pole line is faulted through the transition resistance, and the negative pole line is faulty. If k ₂ W _S f(x ₀₂ )<W _S U _dif <k ₁ W _S f(x ₀₁ ) satisfy ∫U _com ³ <Δ2 at the same time, it is judged that the hybrid DC transmission positive line passes through the transition resistance Fault, the positive line traveling wave protection acts quickly.

Fig. 2 is a schematic structural diagram of a hybrid direct current transmission line traveling wave protection system 200 based on dual tree complex wavelet variation according to an embodiment of the present invention. As shown in FIG. 2 , the hybrid DC transmission line traveling wave protection system 200 based on dual tree complex wavelet variation provided by the embodiment of the present invention includes: a calculation unit 201 , a judging unit 202 and a protection unit 203 . Preferably, the calculating unit 201 is configured to calculate the voltage differential modulus and the voltage common modulus according to the collected positive and negative DC voltages.

Preferably, in the calculation unit 201, the voltage differential modulus and the voltage common modulus are calculated using the following formula:

f(x)=0.5x(U ₁ −U ₂ ),

f ₁ (x)=0.5x(U ₁ +U ₂ ),

Among them, f(x) is the differential modulus of voltage; f ₁ (x) is the common modulus of voltage; U ₁ and U ₂ are the collected positive and negative DC voltages respectively.

Preferably, the judging unit 202 is configured to use a dual tree complex wavelet transform to calculate the voltage differential modulus, and judge whether the protection is activated according to the high sensitivity start judgment basis.

Preferably, in the judging unit 202, the dual tree complex wavelet transform is used to calculate the voltage difference modulus, and whether the protection is started is judged according to the high-sensitivity start judgment basis, including:

The dual tree complex wavelet transform W _S f(x) of the differential modulus is calculated by using the even number complex wavelet transform, and the high sensitivity start judgment basis is used to judge whether W _S f(x)>Δ3 is satisfied, if W _S f(x)> Δ3, it is determined that the protection is activated, and the integral value ∫U _com ³ of the third power of the voltage common mode is calculated; otherwise, it is determined that the protection is not activated; wherein, S is a scaling function; Δ3 is the third preset threshold, which is a positive value.

Preferably, the protection unit 203 is configured to judge the fault according to the dual tree complex wavelet transform of the voltage common modulus and the voltage differential modulus and the corresponding fault extreme value using the fault judgment basis of the hybrid direct current transmission line when it is determined that the protection is started type and perform corresponding protection actions, wherein, the fault judgment basis of the hybrid DC transmission line includes: bipolar fault protection judgment basis, unipolar metallic fault protection judgment basis, unipolar transition resistance fault protection judgment basis and fault selection basis for judgment.

Preferably, the basis for judging the bipolar fault protection is: if W _S f(x)>k ₁ W _S f(x ₀₁ ) holds true, then it is judged as a bipolar fault of the hybrid direct current transmission line. The basis for judging the unipolar metallic fault protection is: if k _{2 WS} f(x ₀₂ )< _WS f(x)<k _{1 WS} f(x ₀₁ ) holds true, then it is judged as a unipolar metallic fault. The basis for judging the unipolar transition resistance fault protection is: if k ₃ W _S f(x ₀₃ )<W _S f(x)<k ₂ W _S f(x ₀₂ ) holds true, then it is judged as unipolar transition resistance Fault. The basis for judging fault pole selection is: if ∫f ₁ ³ (x)>Δ1 holds true, then it is judged as a negative pole fault; if ∫f ₁ ³ (x)<Δ2 holds, then it is judged as a positive pole fault. Among them, f(x) is the voltage difference modulus; W _S f(x) is the dual tree complex wavelet transform of f(x); S is the scaling function, and x ₀₁ is the dual tree complex wavelet transform of the line end bipolar fault Modulus maximum point; W _S f(x ₀₁ ) is the modulus maximum value of the dual tree complex wavelet transform at the line end bipolar fault, k ₁ is the ratio coefficient; x ₀₂ is the dual Modulus maximum point of tree complex wavelet transform; W _S f(x ₀₂ ) is the modulus maximum value of dual tree complex wavelet transform when unipolar fault occurs at the line end; k ₂ is the ratio coefficient; x ₀₃ is the single pole passing through the line end W _S f (x ₀₃ ) is the modulus maximum point of the dual tree complex wavelet transform when the single pole at the end of the line passes through the transition resistance fault; k ₃ is the ratio coefficient; f ₁ (x) is a voltage common mode value, Δ1 is a first preset threshold, which is a positive value; Δ2 is a second preset threshold, which is a negative value.

Preferably, in the protection unit, when it is determined that the protection is started, according to the dual tree complex wavelet transform of the voltage common modulus and the voltage differential modulus and the corresponding fault extreme value, the fault judgment basis of the hybrid direct current transmission line is used to judge the fault type And carry out corresponding protective actions, including:

If W _S f(x)>k ₁ W _S f(x ₀₁ ) holds true, it is judged as a bipolar fault of the hybrid DC transmission line, and the traveling wave protection of the positive and negative poles operates quickly;

If k ₂ W _S f(x ₀₂ )＜W _S f(x)＜k ₁ W _S f(x ₀₁ ) holds true, then it is judged as a unipolar metallic fault, and the polarity of the fault is judged by using the fault pole selection judgment basis , if ∫f ₁ ³ (x)＞Δ1 holds true, it is judged as a negative pole fault, and the negative pole traveling wave protection operates quickly; if ∫f ₁ ³ (x)<Δ2 holds true, it is judged as a positive pole fault, and the positive pole traveling wave protection operates quickly ;

If k ₃ W _S f(x ₀₃ )＜W _S f(x)＜k ₂ W _S f(x ₀₂ ) holds true, it is judged as a unipolar transition resistance fault, and the fault is judged based on the fault pole selection judgment basis polarity, if ∫f ₁ ³ (x)>Δ1 is established, it is judged as a negative pole fault, and the negative pole traveling wave protection acts quickly; if ∫f ₁ ³ (x)<Δ2 is established, it is judged as a positive pole fault, and the positive pole traveling wave Protection for quick action.

The hybrid HVDC transmission line traveling wave protection system 200 based on the dual tree complex wavelet variation in the embodiment of the present invention corresponds to the hybrid DC transmission line traveling wave protection method 100 based on the dual tree complex wavelet variation in another embodiment of the present invention , which will not be repeated here.

The invention has been described with reference to a small number of embodiments. However, it is clear to a person skilled in the art that other embodiments than the invention disclosed above are equally within the scope of the invention, as defined by the appended patent claims.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise therein. All references to "a/the/the [means, component, etc.]" are openly construed to mean at least one instance of said means, component, etc., unless expressly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

Claims (10)

1. A hybrid direct current transmission line traveling wave protection method based on dual tree complex wavelet variation, it is characterized in that, described method comprises: Calculate the voltage differential modulus and voltage common modulus according to the collected positive and negative DC voltages; Use the dual tree complex wavelet transform to calculate the voltage difference modulus, and judge whether the protection is started according to the high sensitivity start judgment basis; When it is determined that the protection starts, according to the dual tree complex wavelet transform of the voltage common modulus and the voltage difference modulus and the corresponding fault extreme value, the fault judgment basis of the hybrid DC transmission line is used to judge the fault type and carry out the corresponding protection action. The fault judgment basis of the hybrid DC transmission line includes: bipolar fault protection judgment basis, unipolar metallic fault protection judgment basis, unipolar transition resistance fault protection judgment basis and fault pole selection judgment basis. 2. method according to claim 1, is characterized in that, utilizes following formula to calculate voltage differential modulus and voltage common modulus: f(x)=0.5x(U ₁ −U ₂ ), f ₁ (x)=0.5x(U ₁ +U ₂ ), Among them, f(x) is the differential modulus of voltage; f ₁ (x) is the common modulus of voltage; U ₁ and U ₂ are the collected positive and negative DC voltages respectively. 3. method according to claim 1, it is characterized in that, described adopt dual tree complex wavelet transform to calculate the dual tree complex wavelet transform of voltage differential modulus, and judge whether protection starts according to the high sensitivity start judging basis, comprising: The dual tree complex wavelet transform W _S f(x) of the differential modulus is calculated by using the even number complex wavelet transform, and the high sensitivity start judgment basis is used to judge whether W _S f(x)>Δ3 is satisfied, if W _S f(x)> Δ3, it is determined that the protection is activated, and the integral value ∫U _com ³ of the third power of the voltage common mode is calculated; otherwise, it is determined that the protection is not activated; wherein, S is a scaling function; Δ3 is the third preset threshold, which is a positive value. 4. The method of claim 1, wherein, The basis for judging the bipolar fault protection is: If W _S f(x)>k ₁ W _S f(x ₀₁ ) holds true, it is judged as a bipolar fault of the hybrid DC transmission line; The basis for judging the unipolar metallic fault protection is: If k ₂ W _S f(x ₀₂ )＜W _S f(x)＜k ₁ W _S f(x ₀₁ ) holds true, it is judged as a unipolar metallic fault; The basis for judging the unipolar transition resistance fault protection is as follows: If k ₃ W _S f(x ₀₃ )＜W _S f(x)＜k ₂ W _S f(x ₀₂ ) holds true, then it is judged as unipolar transition resistance fault; The fault pole selection judgment basis is as follows: If ∫f ₁ ³ (x)＞Δ1 holds true, it is judged as a negative pole fault; If ∫f ₁ ³ (x)<Δ2 is established, it is judged as a positive fault; Among them, f(x) is the voltage difference modulus; W _S f(x) is the dual tree complex wavelet transform of f(x); S is the scaling function, and x ₀₁ is the dual tree complex wavelet transform of the line end bipolar fault Modulus maximum point; W _S f(x ₀₁ ) is the modulus maximum value of the dual tree complex wavelet transform at the line end bipolar fault, k ₁ is the ratio coefficient; x ₀₂ is the dual Modulus maximum point of tree complex wavelet transform; W _S f(x ₀₂ ) is the modulus maximum value of dual tree complex wavelet transform when unipolar fault occurs at the line end; k ₂ is the ratio coefficient; x ₀₃ is the single pole passing through the line end W _S f (x ₀₃ ) is the modulus maximum point of the dual tree complex wavelet transform when the single pole at the end of the line passes through the transition resistance fault; k ₃ is the ratio coefficient; f ₁ (x) is a voltage common mode value, Δ1 is a first preset threshold, which is a positive value; Δ2 is a second preset threshold, which is a negative value. 5. The method according to claim 4, characterized in that, when the protection is determined to start, according to the dual tree complex wavelet transform of the voltage common modulus and the voltage difference modulus and the corresponding fault extremum, the hybrid direct current transmission line is used The basis for fault judgment is to judge the type of fault and take corresponding protection actions, including: If W _S f(x)>k ₁ W _S f(x ₀₁ ) holds true, it is judged as a bipolar fault of the hybrid DC transmission line, and the traveling wave protection of the positive and negative poles operates quickly; If k ₂ W _S f(x ₀₂ )＜W _S f(x)＜k ₁ W _S f(x ₀₁ ) holds true, then it is judged as a unipolar metallic fault, and the polarity of the fault is judged by using the fault pole selection judgment basis , if ∫f ₁ ³ (x)＞Δ1 holds true, it is judged as a negative pole fault, and the negative pole traveling wave protection operates quickly; if ∫f ₁ ³ (x)<Δ2 holds true, it is judged as a positive pole fault, and the positive pole traveling wave protection operates quickly ; If k ₃ W _S f(x ₀₃ )＜W _S f(x)＜k ₂ W _S f(x ₀₂ ) holds true, it is judged as a unipolar transition resistance fault, and the fault is judged based on the fault pole selection judgment basis polarity, if ∫f ₁ ³ (x)>Δ1 is established, it is judged as a negative pole fault, and the negative pole traveling wave protection acts quickly; if ∫f ₁ ³ (x)<Δ2 is established, it is judged as a positive pole fault, and the positive pole traveling wave Protection for quick action. 6. A hybrid DC transmission line traveling wave protection system based on dual tree complex wavelet variation, characterized in that the system comprises: A calculation unit, used to calculate the voltage differential modulus and the voltage common modulus according to the collected positive and negative DC voltages; The judging unit is used to calculate the dual tree complex wavelet transform of the voltage difference modulus by using the dual tree complex wavelet transform, and judge whether the protection is started according to the high-sensitivity start judgment basis; The protection unit is used for judging the fault type according to the dual tree complex wavelet transform of the voltage common modulus and the voltage differential modulus and the corresponding fault extreme value using the fault judgment basis of the hybrid direct current transmission line when the protection is started and performing corresponding protection Action, wherein the fault judgment basis of the hybrid DC transmission line includes: bipolar fault protection judgment basis, unipolar metallic fault protection judgment basis, unipolar transition resistance fault protection judgment basis and fault pole selection judgment basis. 7. The system according to claim 6, characterized in that, in the calculation unit, the following formula is used to calculate the voltage differential modulus and the voltage common modulus: f(x)=0.5x(U ₁ −U ₂ ), f ₁ (x)=0.5x(U ₁ +U ₂ ), Among them, f(x) is the differential modulus of voltage; f ₁ (x) is the common modulus of voltage; U ₁ and U ₂ are the collected positive and negative DC voltages respectively. 8. The system according to claim 6, characterized in that, in the judging unit, the dual tree complex wavelet transform is used to calculate the voltage difference modulus, and judge whether the protection starts according to the high-sensitivity judgment basis ,include: The dual tree complex wavelet transform W _S f(x) of the differential modulus is calculated by using the even number complex wavelet transform, and the high sensitivity start judgment basis is used to judge whether W _S f(x)>Δ3 is satisfied, if W _S f(x)> Δ3, it is determined that the protection is activated, and the integral value ∫U _com ³ of the third power of the voltage common mode is calculated; otherwise, it is determined that the protection is not activated; wherein, S is a scaling function; Δ3 is the third preset threshold, which is a positive value. 9. The system of claim 6, wherein: The basis for judging the bipolar fault protection is: If W _S f(x)>k ₁ W _S f(x ₀₁ ) holds true, it is judged as a bipolar fault of the hybrid DC transmission line; The basis for judging the unipolar metallic fault protection is: If k ₂ W _S f(x ₀₂ )＜W _S f(x)＜k ₁ W _S f(x ₀₁ ) holds true, it is judged as a unipolar metallic fault; The basis for judging the unipolar transition resistance fault protection is as follows: If k ₃ W _S f(x ₀₃ )＜W _S f(x)＜k ₂ W _S f(x ₀₂ ) holds true, then it is judged as unipolar transition resistance fault; The fault pole selection judgment basis is as follows: If ∫f ₁ ³ (x)＞Δ1 holds true, it is judged as a negative pole fault; If ∫f ₁ ³ (x)<Δ2 is established, it is judged as a positive fault; Among them, f(x) is the voltage difference modulus; W _S f(x) is the dual tree complex wavelet transform of f(x); S is the scaling function, and x ₀₁ is the dual tree complex wavelet transform of the line end bipolar fault Modulus maximum point; W _S f(x ₀₁ ) is the modulus maximum value of the dual tree complex wavelet transform at the line end bipolar fault, k ₁ is the ratio coefficient; x ₀₂ is the dual Modulus maximum point of tree complex wavelet transform; W _S f(x ₀₂ ) is the modulus maximum value of dual tree complex wavelet transform when unipolar fault occurs at the line end; k ₂ is the ratio coefficient; x ₀₃ is the single pole passing through the line end W _S f (x ₀₃ ) is the modulus maximum point of the dual tree complex wavelet transform when the single pole at the end of the line passes through the transition resistance fault; k ₃ is the ratio coefficient; f ₁ (x) is a voltage common mode value, Δ1 is a first preset threshold, which is a positive value; Δ2 is a second preset threshold, which is a negative value. 10. The system according to claim 9, characterized in that, in the protection unit, when it is determined that the protection starts, according to the dual tree complex wavelet transform of the voltage common modulus and the voltage difference modulus and the corresponding fault extremum utilization The fault judgment of the hybrid DC transmission line is based on the judgment of the fault type and corresponding protection actions, including: If W _S f(x)>k ₁ W _S f(x ₀₁ ) holds true, it is judged as a bipolar fault of the hybrid DC transmission line, and the traveling wave protection of the positive and negative poles operates quickly; If k ₂ W _S f(x ₀₂ )＜W _S f(x)＜k ₁ W _S f(x ₀₁ ) holds true, then it is judged as a unipolar metallic fault, and the polarity of the fault is judged by using the fault pole selection judgment basis , if ∫f ₁ ³ (x)＞Δ1 holds true, it is judged as a negative pole fault, and the negative pole traveling wave protection operates quickly; if ∫f ₁ ³ (x)<Δ2 holds true, it is judged as a positive pole fault, and the positive pole traveling wave protection operates quickly ; If k ₃ W _S f(x ₀₃ )＜W _S f(x)＜k ₂ W _S f(x ₀₂ ) holds true, it is judged as a unipolar transition resistance fault, and the fault is judged based on the fault pole selection judgment basis polarity, if _∫f1 ³ (x)>Δ1 is established, it is judged as a negative pole fault, and the negative pole traveling wave protection operates quickly ^; Quick action.